Ichneumonoid wasps are important parasites of other insects. Common hosts are larvae and pupae of Coleoptera, Hymenoptera, and Lepidoptera. There are approximately 3,000 species in North America - more than any other Hymenoptera family. One way they differ from the wasps that sting (Scolioidea, Vespoidea and Sphecoidea) is that the antennae are longer, usually with 16 or more segments.

Female ichneumons frequently exhibit an ovipositor longer than their body. Ovipositors and stingers are analogous structures; some Ichneumons inject venom along with the egg, but they do not use the ovipositor as a stinger per se. Stingers are used exclusively for defense; they cannot be used as egg-laying equipment. Males wasps do not have stingers or ovipositors.

In some species of Ichneumon wasps, both sexes will wander over the surface of logs, tree trunks, and even grass stems tapping with their antennae. Each sex does so for a different reason; females are 'listening' for host larvae upon which to lay eggs, males are listening for newly emerging virgin females with which to mate. Upon sensing the vibrations emitted by such insect larvae, the female wasp will drill her ovipositor into the substrate until it reaches the cavity wherein lies the larva. She then injects an egg through the hollow tube into the poor unfortunate's home (sometimes inside the larva itself). There the egg will hatch and the resulting larva will devour its host before emergence.

I found this male ichneumon wasp (subfamily Anomaloninae) as he hunted the forest understory for females. He flitted through the shadows in a bouncing flight; the black wings and black body become quite invisible, and all you see is the yellow antennae and yellow hind legs as 2 pairs of tiny filaments dancing in thin air - it's really a magical sight! I was lucky to catch him while he alighted to clean his abdomen with his back legs - the spurs on the rear legs are used to energetically scrape the abdomen in an (apparently successful) effort to dislodge eggs laid by other parasites. I've seen large Megarhyssa females spend more than 10 minutes cleaning their abdomens and ovipositors before flying off.

You'll often see ichneumons and braconids hunting amidst low foliage; the females hunt for males and then hosts, the males hunt for mates and then they are finished. It's not often you can catch one actually depositing eggs, but it's a really wonderful thing to see; a marvel of efficiency that is the product of millions of years of evolution.

Scientists are still not sure how an ichneumon wasp "drills." It is thought vibration might be involved but no one is sure. I suspect the tip of the terebra is sharp and the wasp forces aside the "soft" tissue of the wood much as you would push a needle into cork. I have seen ovipositors hanging from tree trunks, sans wasp. Evidently, the poor female sometimes flies away without her egg-layer, much as a honeybee commits the ultimate sacrifice in defense of the colony when she leaves her stinger in your arm.

It amazes me. How does that wasp know exactly where and when the egg must be laid? For it must be laid inside the cell of the alien larvae - sometimes laid directly on the body of the prey, sometimes inside the host larva, where it will develop and eat the host from the inside out!

The great Charles Darwin came up against one of the greatest tests of his religious faith when studying the Ichneumonidae and contemplating their seemingly evil and cruel ploy for exploiting other creatures; he thought the monstrosity too evil for God to have thought of it, much less condone it.

He wrote, in 1860, "I own that I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice."

Hymenoptera (Latin for membrane wing) is a vast assemblage of insects second only to Coleoptera (beetles) in the number of described species. Hymenoptera number some 115,000 species - of which 18,000 live in North America. Hymenopterans inhabit a wide variety of habitats, and show an incredible diversity in size, behavior, structure and color. Insects & Spiders | Bees & Wasps Index | Bees & Wasps Main | Beetles Index